西南不同类型紫色土pH变化、重金属累积与潜在生态风险评估

Heavy Metal Accumulation and Assessment of Potential Ecological Risk Caused by Soil pH Changes in Different Types of Purple Soils in Southwest China

施肥在作物增产方面的优势已得到广泛认可,但施肥对西南不同类型紫色土重金属累积与潜在生态风险的长期影响与作用机制尚不清楚.基于连续13a玉米-白菜轮作长期定位试验,采集单施化肥(NPK)、单施有机肥(M)、有机无机配施(NPKM)和不施肥对照(CK)这4个处理的酸性、中性和钙质紫色土,测定各处理土壤理化指标和耕层土壤中Cu、Zn、Cd、Ni、Pb和Cr全量,通过单因子污染指数(Pi)分别计算内梅罗综合污染指数(PN)和潜在生态风险指数(RI),评估长期施肥后土壤重金属污染特征和生态风险,进一步通过偏最小二乘路径模型(PLS-PM)解析土壤理化指标变量与重金属综合污染指数和潜在生态风险的关系.结果表明,土壤理化指标和重金属全量在不同施肥方式和土壤类型下差异显著(P <0.05),且施肥方式的影响程度高于土壤类型.相较于NPK处理,NPKM和M处理土壤有机碳(SOC)、有效钾(AK)和有效磷(AP)含量平均增幅达62.53%~236.07%、105%~505.71%和444.92%~1 269.95%;各施肥处理显著改变酸性和中性紫色土pH,NPK处理下显著降低1.58和1.87,NPKM和M处理下平均上升0.61~1.70.长期施肥后3种不同类型紫色土重金属全量均有提高,NPKM和M处理土壤重金属全量的平均增幅(93.63%和96.39%)高于NPK处理(51.79%).长期施用有机肥后PN更高,其中钙质紫色土M处理PN最高,达中等危害等级,且酸性和中性紫色土中各处理RI高于钙质紫色土,重金属Cd和Pb的污染程度和生态风险更高;对理化因子、PN和RI进行冗余分析结果表明,AP、ΔpH(各施肥处理相较于初始土壤pH变化量)和NO_(3)--N分别解释了方差变异的57.7%、11.2%和9.7%,达到显著水平;PLS-PM分析结果表明,长期施肥通过提高土壤AP和加剧pH变化影响重金属累积导致潜在生态风险增加.研究结果可为紫色土农田养分管理与重金属污染防治提供理论依据.

The advantages of fertilization in increasing crop yield have been widely recognized,but the long-term effect and mechanism of fertilization on heavy metal accumulation and potential ecological risks in different types of purple soil in Southwest China remain unclear.In this study,we conducted a long-term positioning experiment of maize-cabbage rotation for 13 consecutive years.Four treatments,namely,chemical fertilizer application(NPK),organic fertilizer application(M),organic-inorganic combination application(NPKM),and control without fertilizer application(CK),of acidic,neutral,and calcareous purple soil,were established.The soil physicochemical indicators and the total amount of heavy metals in the topsoil of each treatment,including Cu,Zn,Cd,Ni,Pb,and Cr,were measured.The Nemero comprehensive pollution index(PN)and potential ecological risk index(RI)were separately calculated by using the single-factor pollution index(P)i.The characteristics and ecological risks of soil heavy metal pollution after long-term fertilization were evaluated.Furthermore,the relationship between soil physicochemical index variables,comprehensive pollution index of heavy metals,and potential ecological risks were analyzed through the partial least squares path model(PLS-PM).The results showed that the physicochemical indexes of soil and the total amount of heavy metals were significantly different under different application treatments and soil types(P<0.05),and the effect of the application treatment was significantly higher than that of soil type.Compared to that in the NPK treatment,the average increase in soil organic carbon(SOC),available potassium(AK),and available phosphorus(AP)content in the NPKM and M treatments was 62.53%-236.07%,105%-505.71%,and 444.92%-1269.95%,respectively.Each application treatment significantly changed the pH of acidic and neutral purple soil,with a significant decrease of 1.58 and 1.87 under the NPK treatment and an average increase of 0.61-1.70 under the NPKM and M treatments.After long-term fertilization,the total amount of heavy metals in the three different types of purple soil increased.The average increase in the total amount of heavy metals under the NPKM and M treatments(93.63%and 96.39%)was higher than that under the NPK treatment(51.79%).After long-term application of organic fertilizer,the PN was higher,with the highest PN under the M treatment of calcareous purple soil,reaching a moderate hazard level.Moreover,the RI of each treatment in acidic and neutral purple soil was higher than that in calcareous purple soil,and the pollution level and ecological risk of the heavy metals Cd and Pb were higher.The redundancy analysis of physical and chemical factors,PN,and RI showed that AP,ΔpH(relative to the initial soil pH change),and NO_(3)−-N explained 57.7%,11.2%,and 9.7%of the variance variation,reaching a significant level.The PLS-PM analysis results showed that long-term fertilization increased the accumulation of heavy metals by increasing soil AP and exacerbating pH changes,leading to potential ecological risks.The results can provide a theoretical basis for nutrient management and heavy metal pollution prevention in arable land with purple soil.